Photo taken on Jan 12, 2015 shows an overall view of the Jingling Mausoleum for imperial concubines at the Eastern Qing tombs in Zunhua city of North China's Hebei province. [Photo/CFP]

Local authorities confirmed on Tuesday that the Jingling Mausoleum for imperial concubines at the Eastern Qing tombs in Zunhua city of North China's Hebei province was robbed by tomb raiders early on the morning of Oct 31.

So far, police have arrested seven suspects and recovered 12 pieces of stolen cultural relics, including precious jewelry and ancient clothing, according to the official statement.

The Eastern Tombs of the Qing Dynasty (1644-1911) are the largest, most complete and best preserved extant mausoleum complex in China and placed on UNESCO's World Heritage List in 2000.

Construction of the complex, which stretches over a total area of 80 square kilometers, took 247 years to complete after work began in 1661.

Five emperors, 15 empresses, 136 imperial concubines, three princes and two princesses from the Qing Dynasty are buried here.

Villagers who live nearby said that it was not the first time a tomb had been raided in the Eastern Qing tombs.

Local authorities have now tightened up security around the tomb complex.

The case is still under investigation.